There are a wide variety of photomasks known in the art, as well as diverse uses to which they can put, as described in, e.g., U.S. Pat. Nos. 6,472,107 and 6,567,588. Among the many types of photomasks used in the semiconductor industry, binary and phaseshift photomasks are quite common. A typical binary photomask is comprised of a substantially transparent substrate 2 and opaque layer 4, in which a pattern is formed, as shown in a cross sectional illustration of an unprocessed binary photomask in FIG. 1A. Further, the opaque layer 4 may also have an anti reflective (“AR”) coating 6. The pattern of the opaque material in the opaque layer 4 and AR material in the AR coating 6 on the substantially transparent substrate 2 may be a scaled negative of the image desired to be formed on the semiconductor wafer. For a typical chrome on glass (“CoG”) or binary photomask, the substantially transparent substrate 2 is comprised of quartz. The opaque material 4 is comprised of chromium (“Cr”) and the AR material is comprised of chromium oxide (“CrO”).
A binary photomask used in the production of semiconductor devices is formed from a “blank” photomask. As shown in FIG. 1A, a prior art blank photomask 1 is commonly comprised of at least four layers. The first layer 2 is a substantially transparent substrate, such as quartz, commonly referred to as the substrate. The next layer above the substantially transparent layer 2 is an opaque layer 4, which is comprised of Cr in the case of a typical CoG photomasks. Thereafter, although not always necessary, there may be an AR layer 6 integral to the opaque layer, which in the case of CoG photomasks is comprised of CrO. A layer of photosensitive resist material 8 resides as the top layer. In the case of CoG photomasks, the photosensitive resist material 8 is typically a hydrocarbon polymer, the various compositions and thicknesses of which are well known in the art. Other layers may also be present for alternative reasons, as is described, for example, in U.S. Pat. No. 6,472,107. Similarly, other materials may be used as is well known in the art.
The desired pattern of opaque material to be created on the photomask may be defined by an electronic data file loaded into an exposure system which typically scans an electron beam (E beam) or laser beam in a raster fashion across the blank photomask. One such example of a raster scan exposure system is described in U.S. Pat. No. 3,900,737. Other imaging systems can be used that do not use raster scanning, such as shaped vector tools. As the E beam or laser beam is scanned across the blank photomask, the exposure system directs the E beam or laser beam at addressable locations on the photomask as defined by the electronic data file. In the case of a positive photoresist, the areas that are exposed to the E beam or laser beam become soluble, while the unexposed portions remain insoluble. In the case of a negative photoresist, the unexposed areas become soluble, while the exposed portions remain insoluble. As shown in FIG. 1B, after the exposure system has scanned the desired image onto the photosensitive resist material, the soluble photosensitive resist is removed by means well known in the art, and the insoluble photosensitive resist material 8a remains adhered to the next layer (e.g., the AR layer 6).
After undergoing the foregoing photolithographic process, as illustrated in FIG. 1C, the exposed layer of AR material 6 and the underlying layer of opaque material 4 are no longer covered by the photosensitive resist material 8a and are removed by a well known etch process. Only the portions of the layer of AR material 6a and the layer of opaque material 4a residing beneath the remaining photosensitive resist material 8a remain affixed to the substantially transparent substrate 2. This initial or base etching may be accomplished by either a wet etching or dry etch process, both of which are well known in the art.
Another type of photomask used for transferring images to a semiconductor wafer is commonly referred to as a phaseshift photomask. Phaseshift photomasks are generally preferred over binary photomasks when the design to be transferred to the semiconductor wafer includes smaller, tightly packed feature sizes which are below the resolution capabilities of optical equipment being used. Phaseshift photomasks are engineered to be 180 degrees out of phase with light transmitted through etched areas on the photomask so that the light transmitted through the openings in the photomask is equal in amplitude.
One type of phaseshift photomask is commonly referred to as an embedded attenuated phaseshift mask (EAPSM). Other types of phaseshift masks are also known, and the teachings of the present invention may be equally applied thereto. As shown in FIG. 2A, a typical blank EAPSM 31 may be comprised of four layers. The first layer is a typically a substantially transparent material 33 (such as quartz, for example) and is commonly referred to as a substrate. The next layer is typically an embedded phaseshifting material (“PSM layer”) 35, such as molybdenum silicide (MoSi), tantalum silicon nitride (TaSiN), titanium silicon nitride (TiSiN), zirconium silicon oxide (ZrSiO), or other known phase materials. The next layer is typically an opaque material 37, such as chromium, which may optionally include an anti reflective coating such as chromium oxynitride (CrON). The top layer is a photosensitive resist material 39, as is well known in the art.
The method for processing a conventional EAPSM is now described. As with binary photomasks, the desired pattern of the opaque material to be created on the EAPSM is typically scanned by an electron beam (E beam) or laser beam in a raster or vector fashion across a blank EAPSM 31. As the E beam or laser beam is scanned across the blank EAPSM 31, the exposure system directs the E beam or laser beam at addressable locations on the EAPSM. In the case of a positive photoresist material, the areas that are exposed to the E beam or laser beam become soluble, while the unexposed portions remain insoluble. In the case of a negative photoresist, the unexposed areas become soluble, while the exposed portions remain insoluble.
As is done with binary photomasks and as shown in FIG. 2B, after the exposure system has scanned the desired image onto the photosensitive resist material 39, the soluble photosensitive resist material is removed by means well known in the art, and the insoluble photosensitive resist material 39a remains adhered to the opaque material 37. Thus, the pattern to be formed on the EAPSM is formed by the remaining photosensitive resist material 39a. 
The pattern is then transferred from the remaining photosensitive resist material 39a to the opaque layer 37 and PSM layer 35 via well known etching techniques, such as plasma assisted etch described above, by etching away the portions of the opaque layer and PSM layer not covered by the remaining photoresist. After etching is completed, the remaining photoresist material is stripped or removed as shown in FIG. 2C. Other processing steps, such as partial or complete etching of the opaque layer 37a, may be further performed to complete the fabrication of the phaseshift photomask.
Photomasks are used in the semiconductor industry to transfer micro scale images defining a semiconductor circuit onto a silicon or gallium arsenide substrate or wafer and the like. To create an image on a semiconductor wafer, the photomask is interposed between the semiconductor wafer, which includes a layer of photosensitive material, and a stepper, which houses an energy source, such as a lamp or a laser. The energy generated by the stepper passes through the transparent portions of the substantially transparent substrate not covered by the opaque material (and, if utilized, the anti reflective and/or phaseshift material) and causes a reaction in the photosensitive material on the semiconductor wafer. Energy from the stepper is prevented from passing through the opaque portions of the photomask. As with the manufacture of photomasks, when the photosensitive material is exposed to light it will react. Thereafter, the soluble photosensitive material is removed using processes well known in the prior art. The semiconductor wafer is then etched in a manner similar to that described above. After further processing, a semiconductor product is formed.
As semiconductor chip features become exponentially smaller and the number of transistors per device become exponentially larger, large burdens have been placed on lithography processes. Resolution of anything smaller than a wavelength of exposure radiation is generally quite difficult, and pattern fidelity can deteriorate dramatically in sub-wavelength lithography. The resulting semiconductor features may deviate significantly in size and shape from the ideal pattern drawn from the circuit designer. This will decrease process yield and increase cost of the overall photomask manufacturing process.
The semiconductor industry is driven by a desire to lessen processing time and increasing process yield while maintaining or even reducing current costs. In particular, regarding lithograpy techniques using photomasks, the semiconductor industry has attempted to reduce process errors to increase yield by compensating for these process errors in the photomasks themselves. For example, when an image is transferred to a wafer by a 4× stepper tool using a photomask with a critical dimension (CD) of 100 nm, the resulting device layer on the wafer may have a line width of 28 nm. Accordingly, the semiconductor manufacturer will often request that the CD of the photomask be adjusted (or “biased”) so that, when the photomask pattern is developed on the semiconductor wafer, the resulting product will have the desired line width of 25 nm instead of 28 nm.
As a further example, U.S. Patent Application Publication No. 2003/0134205 (“the '205 application”) discloses a process for manufacturing a photomask in which, for each pitch within a semiconductor design, a bias needed at the pitch that maximizes a common process window for all the pitches is calculated based on the given critical dimension (CD) of the mask design. The '205 application combines this biasing with optical proximity correction to appropriately modify the original layout of the photomask. However, techniques such as that disclosed in the '205 application are costly and increase turn-around time due to the required inspection steps and correction analysis.
Other techniques have been adopted to decrease cost of the photomask manufacturing process, which do not relate directly to reducing process errors or increasing yield. Such techniques often involve using multiple mask patterns on a common reticle or plate. For example, U.S. Pat. No. 6,421,111 discloses a multiple image reticle including a two dimensional array of spaced images, which obviates the need for rotation of the reticle to expose various levels of circuitry on a semiconductor wafer.
Similarly, U.S. Patent Application Publication No. 2004/0072083 discloses a photomask including a plurality of mask patterns, each used in an associated photolithography step and corresponding to an associated semiconductor layer, where the mask patterns are arranged so that the photomask is always used oriented in substantially the same direction.
Finally, U.S. Pat. No. 5,604,059 discloses a mask structure including a plurality of duplicating first device patterns and a plurality of duplicating second device patterns. The first device patterns are used to expose a first part of a semiconductor pattern and the second device patterns are used to expose a second part of the semiconductor pattern over the exposed first part.
In none of the prior art references is there disclosed the use of single photomask reticle having multiple versions of the same mask pattern, where different biasing is used.
It is an object of the present invention to provide a reticle that increases process yield and decreases turn-around time by compensating for process errors.
It is a further object of the present invention to provide an improved reticle which has multiple versions of the same mask pattern with different biasing.
Other objects and advantages of the present invention will become apparent from the following description.